docs: def topic_coupling(model, threshold=None, **kwargs):
      """
      Two papers are coupled if they both contain a shared topic above a
      ``threshold``.
  
      Parameters
      ----------
      model : :class:`.LDAModel`
      threshold : float
          Default: ``3./model.Z``
      kwargs : kwargs
          Passed on to :func:`.coupling`\.
  
      Returns
      -------
      :ref:`networkx.Graph <networkx:graph>`
  
      """
      if not threshold:
          threshold = 3./model.Z
      select = lambda f, v, c, dc: v > threshold
  
      graph = coupling(model.corpus, 'topics', filter=select, **kwargs)
      graph.name = ''
      return graph